The invention relates to a method for making a composite metal panel and relates more particularly to a method for making such a panel having precisely located stiffening ribs.
Composite metal panels to be used as structural members or the like in various types of equipment have been provided with selectively stiffened sections in a variety of ways involving a preliminary step of metallurgically bonding a plurality of metal layers together to form a composite metal panel and a subsequent step of deforming at least one of the metal layers to form stiffening sections in the panel. Typically however the conventional methods for making such panels have tended to be inconvenient to carry out or have been subject to deficiencies in precisely locating stiffened sections in the panels relative to each other, in providing stiffened portions of the panel with desired uniform and predetermined strength characteristics, or in introducing stress or weakening factors in carrying out one or more of the process steps. For example in some methods where stiffening ribs are formed by inflating sections of a composite metal panel either with a fluid introduced between layers of the composite under pressure or with a gas developed between the layers by heat-decomposing of inflating material in situ between the layers, there is a tendency for the ribs to be thin in section or to be subject to localized necking down as they are formed by the inflation. Such ribs also typically require elaborate heat treating for achieving desired strength levels after forming. Similarly, in other known methods in which stiffening ribs are formed by folding up individually bonded strip materials or by slitting and folding up partially bonded layer materials, the processes tend to be cumbersome, it is difficult to locate the plurality of ribs in precisely predetermined relation to each other, and the forming steps tend to result in weakening of bonds previously provided in the panels.